As reported in the "New Scientist" (6 August 2005, p. 10) the planet's orbit is also rather eccentric, approaching the Sun within 36 AU--though its orbital period of 560 years means this would not happen very soon. Like Pluto, it seems to be an extreme member of the Kuiper Belt, a population of small planets outside the orbit of Neptune. Most such objects are the size of large asteroids, but according to the same article, two recent additions (one of them announced just a day before the new planet) are about 0.7 time sthe size of Pluto and have inclination of 28°.

For anything else you may want to know about the new planet and its moon (it seems to have one) and those two runners-up, look here, on a web page by Mike Brown, one of the discoverers.

(Concerning Sedna, another newly discovered planet, see
here and here.)